Turbomachines, such as gas turbine engines, typically include a fan section, a turbine section, a compressor section, and a combustor section. The fan section drives air along a core flow path into the compressor section. The compressed air is mixed with fuel and combusted in the combustor section. The products of combustion are expanded in the turbine section.
A typical jet engine has two or three spools, or shafts, that transmit torque between the turbine and compressor sections of the engine. Each of these spools is typically supported by two bearings. One bearing, for example, a ball bearing, is arranged at a forward end of the spool and is configured to react to both axial and radial loads. Another bearing, for example, a roller bearing is arranged at the aft end of the spool and is configured to react only to radial loads. This bearing arrangement fully constrains the shaft except for rotation, and axial movement of one free end is permitted to accommodate engine axial growth.
Epicyclic gearboxes with planetary or star gear trains may be used in gas turbine engines for their compact designs and efficient high gear reduction capabilities. Planetary and star gear trains generally include three gear train elements: a central sun gear, an outer ring gear with internal gear teeth, and a plurality of planet or star gears supported by a carrier between and in meshed engagement with both the sun gear and the ring gear. The gear train elements share a common longitudinal central axis, about which at least two rotate.
During flight, light weight structural cases may deflect with aero and maneuver loads which may cause significant deflection commonly known as backbone bending of the engine. This deflection may result in some misalignment of the gear train elements which may lead to efficiency losses and potential reduced gear life.